Which races for Traveller (canonicity does not matter to me) strike you as good examples of "really alien aliens"?

I'm looking for races that you guys think show one or both of these qualities:

psychology notably different from humans

anatomy and physiology very different from humans

It doesn't matter to me, for purposes of this thread, if the alien race seems playable as a PC or not.

Low-sapient and borderline intelligent races are fine, please do include any you think of.

I know that many of us have different ideas about what is a ''rubber suit'', a ''really alien alien'', an ''animal man'', etc. That's great! It's better that we don't all agree, because this way the thread will likely show greater variety. I don't want to straightjacket things early on by providing strict criteria. Just go with what you read above and let me know which ones you think fit.

This is for building an ATU.

Thanks in advance!

I'm posting this here because it concerns alien races and Contact! seems to be the best sub-forum for such topics even when a specific new race isn't the focus of the thread.